Japanese Patent Application Publication No. 2015-123936 discloses a pneumatic tire comprising a tread portion provided in each block with sipes extending zigzag in the tire axial direction, and the tread pattern is an asymmetrical block-type tread pattern by which the tire mounting location on the vehicle is specified.
In such asymmetrical block-type tread pattern, when the sipes provided in outboard middle blocks located in a middle region of an outboard half tread area are extended to the axially outer edges of the blocks, the rigidity of each block is decreased in its axially outer part, and the steering stability on dry roads is liable to deteriorate.
On the other hand, when a tread block (T) with sipes (s) contacts with the ground (g) as shown in FIG. 8(a), the tread block (T) is deformed, and the edges (e) of the sipes (s) can scratch the road surface.
If the outboard middle blocks are provided with only closed sipes (a type of sipe whose both ends are closed in the block), as the deformation of the block during running on icy roads is decreased as shown in FIG. 8(b), and it is difficult for the sipe edges (e) to effectively scratch the road surface, and the on-ice performance is liable to deteriorate.